4-Bromo-6-(3-(4-chlorophenyl)propoxy)-5-(pyridin-3-ylmethylamino)pyridazin-3(2H)-one mono-hydrochloride represented by the formula (1):
(hereinafter referred to as the compound (I)) is known to show antiplatelet properties and thus expected to be useful as a pharmaceutical product (e.g. Patent Document 1).
On the other hand, it is known that with respect to crystals of organic compounds or their salts, there usually exist crystal polymorphs having different solid structures. Further, it is known that at the time of crystallizing compounds, a solvent or water used for the crystallization is likely to be taken in to form solvate crystals (solvates) or hydrate crystals (hydrates). In this specification, such crystal polymorphs as well as solvate crystals and hydrate crystals will be generally referred to as crystal forms. These crystal forms are usually different from one another in the solubilities, dissolution rates, stabilities, hygroscopicities, melting points, handling properties, etc., and in order to develop a certain crystal of a compound as a pharmaceutical product, it is necessary to consider such characteristics comprehensively and to select a crystal form suitable for the development (e.g. Non-Patent Document 1).
However, with respect to the compound (I), Patent Document 1 discloses only that its melting point is from 188° C. to 205° C., and it discloses nothing about the crystal-form of the compound. Accordingly, in order to develop the compound (I) as a pharmaceutical product, it was necessary to find out the presence of a crystal form of this compound.
Further, in the production of a pharmaceutical product, it is necessary to obtain crystals having the same quality and the same crystal form consistently so that a constant activity and effect can be expected, and, in addition, as its industrial production method, a method is desired wherein a safety aspect is duly taken into consideration for its practical operation. With respect to the compound (I), it is known that the compound can be produced by reacting the corresponding free form with a hydrochloric acid methanol solution in a diethyl ether solvent to form a hydrochloride (e.g. Patent Document 1).
However, there is no disclosure with respect to what kind of crystal form can be obtained by this production method, and further, as an industrial production method, this method has problems such that the hydrogen chloride methanol solution is unstable, and diethyl ether is used which is a special inflammable material belonging to Class 4 of Dangerous Goods. Thus, it was necessary to find out a novel crystal form with respect to the compound (1) and at the same time to establish an industrial production method whereby such a crystal form can selectively be produced.